Next week? According to the AP it will be this weekend, before the two astronauts come home on Monday.

There will be multiple EVAs needed to fully repair the issue. Replacing the PFCS might take two EVAs itself, and refilling the ammonia from spare storage will have to be done separately and will require at least one EVA (and possibly several). The nasaspaceflight.com write-up I'm referencing has a lot more (and more complete) info than the AP story.

I've always found it fascinating that in the cold of space (sort of, the station is in low Earth orbit, I think at about 300km?), things still need to be cooled.

The reason is that there is very little atmosphere at the altitude of the ISS, so it is impossible to cool the station by convection or conduction. I'm pretty sure the ammonia coolant system is used to carry the heat away from the solar panels, where a lot of heat would build up, to radiators.

EDIT: If you're curious, you can check this page for more details. There are a lot more engineering challenges involved for building something in space, but that goes without saying!

In the movie version, they'd come up with a clever plan to generate new ammonia from the urea in their urine with an improvised still than the crew members were secretly using to distill vodka from space fungus etc...and it would all happen in about ten minutes.

I've always found it fascinating that in the cold of space (sort of, the station is in low Earth orbit, I think at about 300km?), things still need to be cooled.

The reason is that there is very little atmosphere at the altitude of the ISS, so it is impossible to cool the station by convection or conduction. I'm pretty sure the ammonia coolant system is used to carry the heat away from the solar panels, where a lot of heat would build up, to radiators.

Yes, you have to think of the ISS as being in the middle of a Thermos bottle, rather than being in the "cold" of space.

I've always found it fascinating that in the cold of space (sort of, the station is in low Earth orbit, I think at about 300km?), things still need to be cooled.

The reason is that there is very little atmosphere at the altitude of the ISS, so it is impossible to cool the station by convection or conduction. I'm pretty sure the ammonia coolant system is used to carry the heat away from the solar panels, where a lot of heat would build up, to radiators.

ahh good point! i never thought about that obvious aspect of space, that there is virtually nothing to make up a manifold and transfer the heat

So you're saying they fixed an actual real-world problem in space by re-routing the power?

OMG, seems I owe ST:TNG a huge apology then .

But they didn't reverse the polarity.

And I say "bounce the graviton particle beam off the main deflector dish"That's the way we do things ladsJust makin' shit up as we wishThe Klingons and the Romulans pose no threat to us!'Cause if we find we're in a bind we just make some shit up. -- Voltaire

... I'm pretty sure the ammonia coolant system is used to carry the heat away from the solar panels, where a lot of heat would build up, to radiators.

1) How would radiators help if there is no atmosphere to conduct away the heat? 2) Assuming you had a pressure suit with no temperature controls, why would humans get "cold" in space if there is no atmosphere to take away your own body heat?

... I'm pretty sure the ammonia coolant system is used to carry the heat away from the solar panels, where a lot of heat would build up, to radiators.

1) How would radiators help if there is no atmosphere to conduct away the heat? 2) Assuming you had a pressure suit with no temperature controls, why would humans get "cold" in space if there is no atmosphere to take away your own body heat?

1) The radiators radiate . Literally - they convert heat into infra-red photons which carry away the energy.2) Your suit will radiate as well. It wouldn't dissipate as much power as a proper radiator, but enough energy will get lost to bring your temperature down very fast.

... I'm pretty sure the ammonia coolant system is used to carry the heat away from the solar panels, where a lot of heat would build up, to radiators.

1) How would radiators help if there is no atmosphere to conduct away the heat? 2) Assuming you had a pressure suit with no temperature controls, why would humans get "cold" in space if there is no atmosphere to take away your own body heat?

Radiators radiate :-), they don't rely (solely) on conduction. The sun heats the earth, yet there is no atmosphere between there and here. Same idea here--use radiators to re-radiate that heat that was absorbed from the sun back out into space.

Same with your 2nd question--there are 3 ways to exchange heat: radiation, conduction and convection. The last 2 rely on other materials to move heat away from the body in question, but radiation doesn't.

Keeping spacecraft and/or astronauts cool and/or warm in the vacuum of space is actually one of those weirdly counter-intuitive things that most people learn incorrectly (along with why people "float" in space). This is probably worth a fun little "Ask Ars" write-up!

... I'm pretty sure the ammonia coolant system is used to carry the heat away from the solar panels, where a lot of heat would build up, to radiators.

1) How would radiators help if there is no atmosphere to conduct away the heat? 2) Assuming you had a pressure suit with no temperature controls, why would humans get "cold" in space if there is no atmosphere to take away your own body heat?

1)Perhaps a source of confusion is that radiators on Earth actually use convection, not infrared radiation, to emit heat. The radiators on the ISS give off infrared radiation in order to lose heat.

2)The human body does not have as much surface area per unit mass as the solar panels on the ISS do. Surface area divided by mass will primarily govern how much your temperature is rising due to solar radiation. As a result, the ISS solar panels need cooling and the human body needs heating.

Edit: I should note that I'm really over-simplifying here. The system of an astronaut is really much more complex because you have to realize that the heat distribution isn't uniform. The side facing away from the sun will be much colder without proper handling of heat inside the suit. I'm only an electrical engineer so I can't give you a full answer, but rest assured that they have more capable people than me designing those space suits!

Edit 2: As has been noted, the human body would actually need cooling too, and I was a little hasty with my response to #2. I suspect, however, that the solar panels still heat up quite a bit faster than an astronaut would.

... I'm pretty sure the ammonia coolant system is used to carry the heat away from the solar panels, where a lot of heat would build up, to radiators.

1) How would radiators help if there is no atmosphere to conduct away the heat? 2) Assuming you had a pressure suit with no temperature controls, why would humans get "cold" in space if there is no atmosphere to take away your own body heat?

1)Perhaps a source of confusion is that radiators on Earth actually use convection, not infrared radiation, to emit heat. The radiators on the ISS give off infrared radiation in order to lose heat.

2)The human body does not have as much surface area per unit mass as the solar panels on the ISS do. Surface area divided by mass will primarily govern how much your temperature is rising due to solar radiation. As a result, the ISS solar panels need cooling and the human body needs heating.

Clearly the NASA guys never played any Battletech, if they did they'd know to pack as many heat sinks as possible.

Phil Plait's Bad Astronomy blog has an entry on this today with another good picture showing the location of the problem, as well as a video where the frozen ammonia flakes can be seen floating away from the truss section.

OT: Nice choice of pic for the article. The station looks beautiful like that, floating above the curve of the Earth, with the shuttle docked.

I've always found it fascinating that in the cold of space (sort of, the station is in low Earth orbit, I think at about 300km?), things still need to be cooled.

Empty space may be as cold as the stretched and so cooled microwave background radiation of ~ 3 K. but locally it is better to think of the radiative thermal equilibrium as a function of distance from the Sun. If you were large and had similar albedo as Earth you would have a surface temperature of ~ 250 K in LEO. (Average Earth surface temperature is actually ~ 290 K, the difference due to the greenhouse atmosphere.)

Since our missions are smaller and suffers from radiative imbalances and what not, complex thermal engineering is a must.

I didn't know ammonia is a better coolant than the anti-freeze. If it is anti-freeze there are stuff to plug a radiator leak permanently like the one I used on my car.

Ammonia is used in the pipes that run outside the ISS because of its extremely low freezing point (-107 F, -77 C). That being said, the cooling system of a car and the cooling system of the ISS are pretty different beasts.

I didn't know ammonia is a better coolant than the anti-freeze. If it is anti-freeze there are stuff to plug a radiator leak permanently like the one I used on my car.

Ammonia is used in the pipes that run outside the ISS because of its extremely low freezing point (-107 F, -77 C). That being said, the cooling system of a car and the cooling system of the ISS are pretty different beasts.

I guess the ammonia on ISS is more pure than the household cleaning grade ammonia most are familiar with. Putting "ISS grade" ammonia in the hands of random joe car owner, err...

2) Assuming you had a pressure suit with no temperature controls, why would humans get "cold" in space if there is no atmosphere to take away your own body heat?

Actually, in sunlight the astronauts get too hot in spacesuits, not to cold. To cool the suits, they use an ice sublimation system. The amount of available ice is a major limitation to EVA times.

Yep, also why things are white, it's not just a fashion statement. Black stuff gets pretty hot in earth orbit.

Actually that white is typically a specific kind of paint. One of the quirks of radiation is emission and absorption are equal for a given wavelength (see [url=http://en.wikipedia.org/wiki/Black_body_radiation]Black Body Radiation[\url]). Thus, a good radiator that can efficiently dump heat to space also absorbs it. The catch is that the wavelength of radiation is dependent on the temperature of the object radiating (see link above - Plank's and Wien's Laws).

The sun radiates at a very high temperature (~5800K) which is in the UV range. The paint is white because its highly reflective for these wavelengths to minimize absorption of energy. That same paint, in the IR spectrum, is 'black' with a very high emissivity/absorptivity to make it more efficient at dumping heat. The IR 'color' is adjusted based on the planned operating temperature of the radiator.

This is also why satellites and spacecraft use [url=http://en.wikipedia.org/wiki/Multi-layer_insulation]MLI[\url]. The metalized mylar is highly reflective across most of the spectrum. The vacuum between layers and poor conductivity mean that energy must radiate between layers to enter/escape. The high reflectivity limits emission and prevents absorption - so energy from the inside can't get out (when facing dark space) and solar radiation can't get in.

But then why is it better to concentrate the heat into radiators that supposedly have a smaller surface area than the panels themselves, if the main mean of cooling is by surface radiation? Surely this is something aerospace engineers have thought about, but I'd love to see an explanation for my own sake.

I didn't know ammonia is a better coolant than the anti-freeze. If it is anti-freeze there are stuff to plug a radiator leak permanently like the one I used on my car.

Ammonia is used in the pipes that run outside the ISS because of its extremely low freezing point (-107 F, -77 C). That being said, the cooling system of a car and the cooling system of the ISS are pretty different beasts.

I guess the ammonia on ISS is more pure than the household cleaning grade ammonia most are familiar with. Putting "ISS grade" ammonia in the hands of random joe car owner, err...

Sorry folks, I got mix-up the anti-freeze is actually an anti-overheat stuff for the car against its boiling point from over heating and this fine grade of Ammonia is truly an anti-freeze agent against the freezing temperature of the space. :-)